JPH10121185A - Method for casting gray cast iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for casting a high strength gray cast iron. SOLUTION: Casting is carried out under the conditions that the contents of carbon and silicon are set at 2.3-3.2% and 1.2-4.0%, respectively, and an inoculant containing >=20% silicon and >=1% calcium is used by 0.3-0.7% based on cast iron and components other than carbon and silicon are contained so that ΔT3 becomes 5-70 deg.C and the value of ΔT1 /ΔT3 becomes >=0.6 and also the innoculant is added. At this time, ΔT3 is a temp. difference between graphite eutectic temp. of cast iron and cementite eutectic temp., and ΔT1 , is a temp. difference between euetctic supercooling temp. and cementite eutectic temp. By performing casting so that the aforesaid conditions are satisfied, a cast product of gray cast iron having high strength, free from occurrence of chill, and excellent in quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for casting gray cast iron, and more particularly to a method for casting gray cast iron capable of obtaining high strength gray cast iron.

[0002]

2. Description of the Related Art For example, if the strength of gray cast iron used for an engine block or the like is increased and the thickness of a cast product is reduced, the product can be reduced in weight. Current worldwide gray cast iron standard is strength have been made in the range of ^{100N / mm 2 ~350N / mm 2} , it has not been standardized for more strength. The reason is that gray cast iron having a higher strength cannot be stably manufactured, and 400 N / mm ²
A method for stably producing gray cast iron having the above strength is desired.

[0003] At present, methods for improving the tensile strength of gray cast iron include reducing the carbon content of cast iron, reducing the amount of graphite in the structure, inoculating the graphite into A-type graphite, or reducing the carbon content of Ni. It is generally known that Cr, Mo, Cu, etc. are added to cast iron to strengthen the base structure.

[0004]

However, when the carbon content of cast iron is reduced, the components can approach the steel and the strength can be increased, but on the contrary, the amount of graphite in the core structure is reduced, so that graphite is reduced. Reduces the nucleation ability and increases the generation of chill structures called redebrite. Then, due to the generation of the chill structure, the location of occurrence becomes hard and brittle,
Unfavorable results for cast products.

[0005] Conventional inoculation is considered to have little effect even if the inoculation is performed excessively. On the contrary, it is considered that casting defects such as deterioration of mechanical properties of cast products and shrinkage are caused. The inoculum amount in actual production was limited to 0.3% based on the weight of the molten metal. Therefore, the lower the carbon content in the molten metal, the more difficult it is to crystallize A-type graphite, and the lower the carbon content, the more easily undissolved graphite nuclei present in the molten metal are lost. There is a problem that the rate of disappearance of various nuclear materials, that is, fading becomes too fast.

[0006] Further, when Ni, Cr, Mo, Cu, etc. are used as additives, they are also 400 N / mm.
It is not possible to stably obtain a strength of ² or more, and these elements are chilled elements, which causes a problem of generating a chill structure in the product as described above. There is also a spheroidal graphite cast iron in which the shape of graphite is changed from flake to spherical, but this has a problem that its vibration absorbing ability is poor and its advantage as gray cast iron is impaired.

[0007]

Accordingly, the present inventors have conducted various experiments to increase the strength of gray cast iron. In particular, the carbon content, silicon content, inoculation conditions, graphite eutectic temperature, cementite Focusing on eutectic temperature, eutectic supercooling temperature, etc., the invention of the following casting method was completed.

That is, the carbon content is 2.3% to 3.2%.
%, Silicon content is set to 1.2% to 4.0%, and an inoculant containing 20% or more of silicon and 1% or more of calcium is used in a range of 0.3 to 0.7% with respect to cast iron. , And
T ₃ in the range of 5 to 70 ° C., and △ T ₁ / △ value of T ₃ is contain components other than carbon and silicon such that 0.6 or more, and in a condition that is added inoculum I decided to cast it. Here, ΔT ₃ is the temperature difference between the graphite eutectic temperature and the cementite eutectic temperature of cast iron, and ΔT ₁ is the temperature difference between the eutectic supercooling temperature and the cementite eutectic temperature.

[0009] By satisfying the above conditions, it is possible to obtain a gray cast iron cast product having high strength and good quality without chilling.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for casting gray cast iron according to the present invention will be described below.

An experiment on gray cast iron was performed under the following conditions.

First, the content of components other than carbon in cast iron is S
i is 1.7%, Mn is 0.75%, Po is 0.07%,
S is 0.05%, and the carbon content is 2.0% to 3.5%.
Arbitrarily varied between Further, an inoculant containing 15% of Ca, 50% of Si and the balance of Fe was added to the molten metal at 0.3%.
% To 0.7% optionally changing the amount between of △ T ₁ /
The value of ΔT ₃ was set, and the strength of the cast iron at that time was measured.

The results are shown in FIG. As shown in FIG. 1, when the carbon content is 2.3%, the generation of chill structure can be suppressed by setting ΔT ₁ / ΔT ₃ to 0.6 or more. However, when the carbon content is 2.3% or less, ΔT ₁
Regardless of the value of / ΔT ₃ , generation of chilled tissue cannot be suppressed. From this result, it is understood that the carbon content is required to be 2.3% or more. On the other hand, the inclusion of carbon or 3.2%, setting how the value of _{△ T 1 / △ T 3 400N} /
The value of mm ² or more was not obtained, and the strength was insufficient.

A specific experimental method will be described below. The cast iron was melted in a high-frequency induction furnace having a melting amount of 50 kg and a frequency of 3 kHz, and the graphite eutectic temperature, cementite eutectic temperature, and eutectic supercooling temperature of the melted cast iron were measured using Japanese Patent Application No. Hei 7-14409.
No. 9 was used to determine the properties of the molten cast iron. For the measurement, a part of the molten metal was poured into a 3 cup meter, and the eutectic supercooling temperature, cementite eutectic temperature, and graphite eutectic temperature were determined from the temperature change of the injected molten metal. The temperature difference ΔT ₁ between the cementite eutectic temperature and the temperature difference ΔT ₃ between the graphite eutectic temperature and the cementite eutectic temperature were determined. Further, the molten metal was poured into a 30 × 600 mm round bar casting sand mold, and the tensile strength of each cast iron was measured by a tensile tester (not shown).

FIG. 2 shows the relationship between ΔT ₁ / ΔT ₃ and the shape of graphite. When the value of ΔT ₁ / ΔT ₃ is increased, the proportion of A-type graphite increases, and a cast iron having a good carbon shape can be obtained. The vertical axis of the graph of FIG.
It is.

(Equation 1) H = A% × 1.2 + E% × 0.9 + B% × 0.9 + D% × 0.3
+ Chill% × 0 FIGS. 3A to 3D show graphite shapes from A type to D type, respectively.

Further, even if the graphite shape is A type, ΔT ₁
When the value of / ΔT ₃ was 0.5 or more, a better shape was obtained, and improvement in tensile strength was observed.

In FIG. 3, the value of ΔT ₁ / ΔT ₃ is set to 0.
In the determination of the structure with a microscope or the like when the number is 6 or more, the structure of the graphite is almost A-type, and it was conventionally impossible to determine the quality of the graphite structure further. Therefore, Equation 1
H asymptotically approaches 120 when the value of ΔT ₁ / ΔT ₃ is 0.6 or more. In contrast, the strength of cast iron shown in FIG. 1, △ T ₁ / △ with increasing of T ₃ are proportionally increased, △ T ₁ / △ T ₃ is better graphite shape, or intensity of cast iron Is shown.

As described above, in order to stably produce high-strength gray cast iron, it is necessary to accurately determine the graphite shape before the furnace, and to determine the ΔT ₁ / ΔT ₃ value of the cast iron before the furnace. The technique of making the determination is an important element of the present invention.

Next, FIG. 4 shows the results of an experiment conducted on the change in tensile strength and ΔT ₁ / ΔT ₃ when the inoculant addition ratio was changed.

In this experiment, C3.0%, Si1.7%,
Fe-50% Si, Fe-1% Ca- were added to the cast iron having the components of Mn 0.75%, P 0.07% and S 0.05%.
50% Si, Fe-10% Ca-50% Si, Fe
Four kinds of inoculants of -30% Ca-50% Si were added in different amounts, and the values of ΔT ₁ / ΔT ₃ and the strength of cast iron were measured.

According to FIG. 4, first, when Ca is included in the inoculant in an amount of 1% or more, the graphite shape becomes better and the ΔT
The value of ₁ / ΔT ₃ is set to 0.6 or more and 400 N / mm
^In order to achieve ² or more, it was found that the inoculant needed to contain 1% or more of Ca and 20% or more of Si.

Further, in addition to the above examples, Ni, Cr, Mo,
By adding an alloy such as Cu and Ni to strengthen the matrix, it is possible to produce cast iron with increased strength.

[0024]

According to the method for casting gray cast iron of the present invention, the cast iron contains 2.3 to 3.2% of carbon, 1.2 to 4.0% of Si, and 0.1% of Ca. Above, Si is 2
The inoculant containing 0% or more is added to cast iron at 0.3% or more, and the difference between graphite eutectic temperature and cementite eutectic temperature (ΔT ₃ ) is in the range of 5 ° C to 70 ° C by adding components other than carbon and silicon. And the difference between the eutectic supercooling temperature and the cementite eutectic temperature (ΔT ₁ ) divided by the difference between the graphite eutectic temperature and the cementite eutectic temperature (ΔT
₁ / △ T ₃ ) is set to 0.6 or more, and casting is performed. Therefore, the amount of carbon can be reduced and a high-strength cast iron can be stably provided.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the value of ΔT ₁ / ΔT ₃ and tensile strength.

FIG. 2 is a graph showing the relationship between the value of ΔT ₁ / ΔT ₃ and graphitization.

FIG. 3A is a view showing a graphite shape of A type. (B) It is a figure which shows the graphite shape of Etype. (C) It is a figure which shows the graphite shape of Btype. (D) It is a figure which shows the graphite shape of Dtype.

FIG. 4 is a graph showing the relationship between the amount of inoculant added, the value of ΔT ₁ / ΔT ₃ and the tensile strength.

Claims (1)

[Claims] 1. A carbon content of 2.3% to 3.2%, a silicon content of 1.2% to 4.0%, and a content of the carbon and components other than the silicon are determined by a graphite eutectic temperature. Temperature difference ΔT ₃ between eutectic temperature and eutectic temperature is 5
C. to 70.degree. C., and an inoculant containing 20% or more of silicon and 1% or more of calcium is added in a weight ratio of 0.3 to 0.7%. It is characterized in that the used amount of the inoculant is set and cast so that a value obtained by dividing a temperature difference ΔT ₁ between the supercooling temperature and the cementite eutectic temperature by the temperature difference ΔT ₃ is 0.6 or more. Casting method of gray cast iron.